In a frequency hopping (or channel hopping) mesh network, devices communicate using different frequencies/channels at different times. To communicate a packet, a transmitter-receiver pair must be configured to the same channel during packet transmission. For a transmitter to communicate with a receiver at an arbitrary time in the future, the transmitter and receiver must synchronize to a channel schedule that specifies what channel to communicate on at what time. Channel schedules may be assigned to each transmitter-receiver pair independently so that neighboring transmitter-receiver pairs can communicate simultaneously on different channels. Alternatively, all devices in a network may synchronize with a single channel schedule such that all devices transmit and receive on the same channel at any time.
A network discovery system generally requires two functions. First, a discovery protocol is needed between a device within a network and a device attempting to join the network that allows joining devices to passively listen or actively probe for neighboring networks. To support passive listening, devices in a network transmit beacons periodically to announce the presence of a network, while to support active probing, joining devices transmit messages to devices within the network to request a beacon transmission. Second, a network discovery system generally requires a dissemination protocol to communicate network-wide parameters used for the network join process to all devices in the network, such as a network name, access-control security parameters, and/or an indication of network size to allow load balancing across networks.
Current discovery protocols cannot utilize synchronized transmissions since the devices are not synchronized to the frequency hopping schedule of the network or any individual device within the network. Instead, the devices are forced to utilize more expensive unsynchronized transmissions. Also, having every node transmit network discovery beacons with a fixed period is problematic in dense environments since the channel utilization is proportional to network density. In addition, having all nodes that receive a beacon request respond to the request with a transmitted beacon results again in the channel utilization generated by the response being proportional to network density.